1. Field of the Invention
The present invention relates generally to electrical circuits, and more specifically to an improved method and associated power supply circuit that provides circuit protection from AC line noise, transient electromagnetic interference, EMI, and RFI.
2. Discussion of the Related Art Including Information Disclose under 37 CFT 1.97 and 37 CFR 1.98
Switched-mode power supplies make use of power transistors or power MOSFETs and typically require the use of a control module. However, the purpose and operation of the semi-conductor switches and of the control module are entirely different from that in the present invention. The primary purpose of a switched-mode circuit is that of voltage regulation, while the primary purpose of the inventive circuit is noise and transient isolation.
Switching supplies eliminate the need for a main power transformer and large storage filter capacitors. Instead they rectify voltage directly from the AC input and store DC in a small capacitor. Then, current is released in pulses by a transistor—controlled by a PWM (pulse width modulated) controller.
Switched-mode supplies have the advantages of light weight, small size and high efficiency. However, they may not be suitable when the primary requirement for the power supply is low noise. The high frequency switching harmonics generated by such a supply require extensive filters to achieve a low noise ratio. In addition, switched-mode supplies do not block line-noise or transients as in the inventive circuit. When the switched-mode rectifiers are in a conduction state and the switching transistor is on, input line noise may pass through to the output. Additionally, the line-connected rectifiers generate significant power harmonics that are kicked-back onto the power line.
Switched-mode supplies do not utilize dual parallel current paths as in the inventive circuit. However, the inventive concepts herein could be added or adapted to various switched-mode designs, which would give them noise-blocking capabilities.
“Synchronous rectification” circuits such as those disclosed in U.S. Pat. Nos. 6,188,592, 5,818,704, 6,252,781 and 6,256,214 may bear some cursory resemblance to the inventive circuit. However, they are similar only in that their fundamental operation requires two controlled switch elements, such a power MOSFET. They do not utilize dual parallel current paths as in the inventive circuit.
Synchronous rectifiers are usually used in DC-DC voltage conversion where the circuit is designed to convert a DC voltage to a lower voltage. A primary example is the “Buck converter”. However, the purpose of synchronous rectifiers is to convert voltage, while the purpose of the inventive circuit is noise and interference isolation.